Optical displacement sensor and external force detecting device

ABSTRACT

An optical displacement sensor comprises: a light source; a light receiving means adapted to receive light emitted from the light source; and a light diffracting element disposed between the light source and the light receiving means. The light receiving means include a first light receiving element group centrally located, and a second light receiving element group constituted by two separate clusters disposed so as to sandwich the first light receiving element group, and the light diffracting element functions to diffract the light emitted from the light source along one direction of the two-axis directions into a zero-order beam to be received at the first light receiving element group, and higher-order beams received at the second light receiving element group.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical displacement sensor and anexternal force detecting device, and particularly to an opticaldisplacement sensor which detects relative displacement between areference object and a measurement object based on displacement of alight reception position, and further to an external force detectingdevice which detects an external force applied to the measurement objectbased on a signal outputted from the optical displacement sensor.

2. Description of the Related Art

An external force detecting device, such as a six-axis optical forcesensor, is conventionally known, in which a displacement amount of anaction section to receive an external force, namely a measurementobject, relative to a support section to support the action section,namely a reference object, is detected by an optical displacementsensor, and an external force applied to the action section is measuredaccording to an output signal from the optical displacement sensor.

For example, a six-axis optical force sensor comprises opticaldisplacement sensors to measure a six-axis direction displacement, basedon which a six-axis force is calculated. Specifically, such a six-axisoptical force sensor comprises three optical displacement sensors, eachof which uses an optical sensor unit and is capable of measuring atwo-axis (X and Y) direction displacement, thereby enabling measurementof a six-axis direction displacement. The optical sensor unit comprisesa light emitting diode (LED) as a light source and a photodiode (PD)assembly as a light receiving element, such that the LED opposes the PDassembly with their respective optical central axes aligned to eachother. The PD assembly is composed of four PD's and receives lightemitted from the LED at its center area equally shared by the four PD's,whereby displacement of light receiving position at the PD assembly,that is to say relative positional displacement between a componentattached to the LED and a component attached to the PD assembly can bedetected in the optical displacement sensor. In the six-axis opticalforce sensor, a six-axis force applied between the component attached tothe LED and the component attached to the PD assembly is measuredaccording to an output signal from each of the optical displacementsensors.

FIG. 1 is a plan view of a conventional six-axis force sensor asdisclosed in Japanese Patent Application Laid-Open No. H03-245028. Asix-axis force sensor 101 shown in FIG. 1 is structurally composed of acylindrical main body, and top and bottom lids (not shown). The mainbody is constituted basically by a frame 105, which integrally includes:a cylindrical support section 102; an action section 103 locatedcentrally inside the support section 102 and adapted to receive anexternal force; and three elastic spoke sections 104 crookedlystructured so as to be duly deformed elastically in all directions andsupportably connecting the action section 103 to the support section102. The frame 105 is made of a single piece of an aluminum alloymaterial and shaped by cutting and electric discharge machining. Thesupport section 102 and the action section 103 are fixedly attachedrespectively to two components to which a measurement force is applied,and when a force applied acts on the six-axis force sensor 101structured as described above, a micro-displacement with respect tothree-axis direction and a micro-rotation with respect to three-axisrotational direction are generated between the support section 102 andthe action section 103.

The six-axis force sensor 101 further includes three light sources 106disposed at the inner circumference of the support section 102 at 120degree intervals (i.e. at an equi-angular distance), and three opticalsensors (light receiving elements) 108 disposed at the action section103 at 120 degree intervals (i.e. at an equi-angular distance) so as tooppose respective three light sources 106 with mutual optical axesaligned to each other. Each optical sensor 108 and each light source 106disposed opposite to the optical sensor 108 make up an optical sensorunit (optical displacement sensor) 109.

FIG. 2 is an explanatory perspective view of the optical sensor unit(optical displacement sensor) 109 of FIG. 1. As shown in FIG. 2, each ofthe optical sensors 108 is constituted by a PD assembly composed of fourPD's 108 a. The light sources 106 disposed so as to oppose respectiveoptical sensors 108 are each constituted by an infrared high-intensityLED with a pinhole aperture provided at its front face, and lightemitted from the LED 106 and passing through the pinhole aperturepropagates diffusedly and impinges on the center portion of the opticalsensor 108 so as to be substantially equally irradiated on all the fourPD's 108 a. If the support section 102 and the action section 103 aredisplaced relative to each other by an external force, then the lightemitted from the LED 106 is irradiated unequally on the four PD's 108 a,and light amounts received at respective four PD's 108 a are measuredfor calculation of relative displacements with respect to X- and Y-axisdirections. And, the six-axis force sensor 101 calculates forces withrespect to six-axis directions according to the above-calculatedrelative displacements, and a signal is outputted therefrom.

However, the aforementioned conventional optical displacement sensor,and the aforementioned six-axis force sensor, i.e., external forcedetecting device, incorporating the conventional optical displacementsensor has the following problems when respective optical axes of theLED 106 as the light source, and PD assembly 108 to receive lightemitted from the LED 106 are aligned to each other. Specifically, in thealignment work, while positional adjustment with respect to the X- andY-axis directions is easy, rotational adjustment about a Z-axisperpendicular to the X- and Y-axes (to precisely bring the cross-shapedboundary formed by the four PD's 108 a in line with the X- and Y-axes)is very difficult

Conventionally, the rotational adjustment has to be carried out suchthat an LED and a PD assembly are tentatively arranged, and misalignmentin the rotational direction about the Z-axis is checked and correctedbased on a signal from the PD assembly, which is gained by causing anaction section at which either the LED or the PD assembly is disposed tobe displaced in the X- and Y-axis directions. This involves a lot ofworks, and requires an immense amount of time and effort, especiallywhen displacement amount is large.

SUMMARY OF THE INVENTION

The present invention has been made in light of the above problem, andit is an object of the present invention to provide an opticaldisplacement sensor, and an external force detecting device, in which aposition of a light receiving means relative to a light source withrespect to a rotational direction about an optical axis of light emittedfrom the light source can be adjusted easily in a reduced time.

In order to achieve the above object, according to a first aspect of thepresent invention, an optical displacement sensor comprises: a lightsource disposed at one of a reference object and a measurement object; alight receiving means disposed at the other one thereof at which thelight source is not disposed, and adapted to receive light emitted fromthe light source thereby measuring displacement of the measurementobject relative to the reference object with respect to two-axisdirections in a plane perpendicular to an optical axis of the lightemitted from the light source; and a light diffracting element disposedbetween the light source and the light receiving means. The lightreceiving means includes a first light receiving element group centrallylocated, and a second light receiving element group constituted by twoseparate clusters disposed so as to sandwich the first light receivingelement group, and the light diffracting element functions to diffractthe light emitted from the light source into a zero-order beam, andhigher-order beams along one direction of the two-axis directions, suchthat the zero-order beam is received at the first light receivingelement group, and the higher-order beams are received at the secondlight receiving element group.

According to a second aspect of the present invention, an opticaldisplacement sensor comprises: a light source disposed at one of areference object and a measurement object; and a light receiving meansdisposed at the other one thereof at which the light source is notdisposed, and adapted to receive light emitted from the light sourcethereby measuring displacement of the measurement object relative to thereference object with respect to two-axis directions in a planeperpendicular to an optical axis of the light emitted from the lightsource. The light emitted from the light source, at least when receivedat the light receiving means, has its intensity distribution shaped inan oval configuration with two symmetry axes oriented so as to match thetwo-axis directions, respectively, with respect to which thedisplacement of the measurement object relative to the reference objectis measured.

According to a third aspect of the present invention, an opticaldisplacement sensor comprises: a light source disposed at one of areference object and a measurement object; a reflector member disposedat the other one thereof at which the light source is not disposed; alight receiving means disposed at the one object at which the lightsource is disposed, and adapted to receive light which is emitted fromthe light source and which impinges on the reflector member to bereflected backward, thereby measuring displacement of the measurementobject relative to the reference object with respect to two-axisdirections in a plane perpendicular to an optical axis of the lightemitted from the light source,; and a light diffracting element disposedat an optical path from the light source to the light receiving meansvia the reflector member. The light receiving means includes a firstlight receiving element group centrally located, and a second lightreceiving element group constituted by two separate clusters disposed soas to sandwich the first light receiving element group, and the lightdiffracting element functions to diffract the light emitted from thelight source into a zero-order beam, and higher-order beams along onedirection of the two-axis directions, such that the zero-order beam isreceived at the first light receiving element group, and thehigher-order beams are received at the second light receiving elementgroup.

According to a fourth aspect of the present invention, an opticaldisplacement sensor comprises: a light source disposed at one of areference object and a measurement object; a reflector member disposedat the other one thereof at which the light source is not disposed; anda light receiving means disposed at the one object at which the lightsource is disposed, and adapted to receive light which is emitted fromthe light source and which impinges on the reflector member to bereflected backward, thereby measuring displacement of the measurementobject relative to the reference object with respect to two-axisdirections in a plane perpendicular to an optical axis of the lightemitted from the light source. The light emitted from the light source,at least when received at the light receiving means, has its intensitydistribution shaped in an oval configuration with two symmetry axesoriented so as to match the two-axis directions, respectively, withrespect to which the displacement of the measurement object relative tothe reference object is measured.

In the second or fourth aspect of the present invention, the lightsource may be constituted by a light emitting diode (LED), and acylindrical lens may be disposed between the LED and the light receivingmeans whereby the light emitted from the LED has its intensitydistribution turned into the oval configuration with two symmetry axes.

In the first to fourth aspects of the present invention, the lightreceiving means may be structured to be rotatable about the first lightreceiving element group.

According to a fifth aspect of the present invention, there is provideda method of adjusting such an optical displacement sensor as structuredaccording to the first aspect of the present invention. The methodcomprises a step of adjusting a position of the light receiving meansrelative to the light source with respect to a rotational directionabout the optical axis of the light emitted from the light source basedon a reception state of the higher-order beams at the second lightreceiving element group. Consequently, the optical displacement sensorcan be adjusted without troublesome work in a reduced time.

According to a sixth aspect of the present invention, there is provideda method of adjusting such an optical displacement sensor as structuredaccording to the second aspect of the present invention. The methodcomprises a step of adjusting a position of the light receiving meansrelative to the light source with respect to a rotational directionabout the optical axis of the light emitted from the light source basedon a reception state of the light at the light receiving means.Consequently, the optical displacement sensor can be adjusted easilywithout provision of the light diffracting element and the second lightreceiving element group used in the first aspect.

According to a seventh aspect of the present invention, there isprovided a method of adjusting such an optical displacement sensor asstructured to the third aspect of the present invention. The methodcomprises a step of adjusting a position of the light receiving meansrelative to the light source with respect to a rotational directionabout the optical axis of the light emitted from the light source basedon a reception state of the higher-order beams at the second lightreceiving element group. Consequently, the optical displacement sensorstructured to include the reflector member can be also adjusted withouttroublesome work in a reduced time.

According to an eighth aspect of the present invention, there is providea method of adjusting such an optical displacement sensor as structuredaccording to the fourth aspect of the present invention. The methodcomprises a step of adjusting a position of the light receiving meansrelative to the light source with respect to a rotational directionabout the optical axis of the light emitted from the light source basedon a reception state of the light at the light receiving means.Consequently, the optical displacement sensor provided with thereflector member can be adjusted easily without provision of the lightdiffracting element and the second light receiving element group used inthe third aspect.

According to a ninth aspect of the present invention, an external forcedetecting device is provided which incorporates an optical displacementsensor structured according to any one of the aforementioned first tofourth aspects, and an external force applied to a measurement object isdetected based on a signal containing a measurement result by theoptical displacement sensor. In the ninth aspect of the presentinvention, the optical displacement sensor may be provided in a pluralnumber, and a plurality of optical displacement sensors may detectrespective displacements with respect to two-axis directions differentfrom one another. Since the external force detecting device incorporatesthe optical displacement sensors according to the present invention, theadjustment work about the device can be performed easily in a reducedtime.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a conventional six-axis force sensor;

FIG. 2 is an explanatory perspective view of a conventional opticalsensor unit (optical displacement sensor) shown in FIG. 1;

FIG. 3 is an explanatory perspective view of a structure of an opticaldisplacement sensor according to a first embodiment of the presentinvention;

FIG. 4 is a plan view of a light receiving face of a PD assembly shownin FIG. 3;

FIGS. 5A to 5F are explanatory views of adjustment in a rotationaldirection about a Z-axis performed based on positional relation betweenthe light receiving face of the PD assembly of FIG. 4 and respectivebeams (zero-order beam, +first-order beam, and −first-order beam),wherein FIG. 5A to 5C show positional relation examples, and FIG. 5D to5F show adjustment directions about the Z-axis in respective positionalrelations shown by FIGS. 5A to 5C;

FIG. 6 is a plan view of a light receiving face of another PD assemblydifferent from that shown in FIG. 4;

FIG. 7 is an explanatory perspective view of a structure of an opticaldisplacement sensor according to a second embodiment of the presentinvention;

FIG. 8 is a plan view of a light receiving face of a PD assembly shownin FIG. 7;

FIGS. 9A to 9F are explanatory views of adjustment in a rotationaldirection about a Z-axis performed based on positional relation betweenthe light receiving face of the PD assembly of FIG. 8 and respectivebeams (zero-order beam, +first-order beam, and −first-order beam),wherein FIG. 9A to 9C show positional relation examples, and FIG. 9D to9F show adjustment direction about the Z-axis in respective positionalrelations shown by FIGS. 9A to 9C; and

FIG. 10 is an explanatory perspective view of a structure of an opticaldisplacement sensor according to a third embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will hereinafter bedescribed with reference to the accompanying drawings. In theembodiments described below, an optical displacement sensor according tothe present invention is applied to such a six-axis optical force sensoras shown in FIG. 1, but the present invention is not limited toapplication to an external force detecting device for detecting six-axisforce.

A first embodiment of the present invention will be described withreference to FIGS. 3 to 6. Referring first to FIG. 3, an opticaldisplacement sensor comprises: a photodiode (PD) assembly 1 as a lightreceiving means; a light emitting diode (LED) 2 which is a lightemitting element as a light source; a light diffracting element 3 todisperse one beam into three beams; and a lens 4 to shape and condensebeams.

In the optical displacement sensor shown in FIG. 3, the PD assembly 1 ismounted at one of a reference object and a measurement object, and theLED 2 is mounted at the other one thereof, at which the PD assembly 1 isnot mounted, wherein light emitted from the LED 2 is received at the PDassembly 1, and the positional displacement of the measurement objectrelative to the reference object with respect to two-axis directions ina plane perpendicular to the optical axis of the light emitted from theLED 2 is measured on the basis of the state of light reception at the PDassembly 1. This applies to optical displacement sensors according toother embodiments of the present invention shown in FIGS. 2 and 10.

The light emitted from the LED 2 is dispersed by the light diffractingelement 3 into three beams. Here, the three beams are respectivelyreferred to as; a zero-order beam that is positioned at the middle; a+first-order beam that is positioned on the right when facing the lightreceiving face of the PD assembly 1; and a −first-order beam that ispositioned on the left when facing the light receiving face of the PDassembly 1.

The light diffracting element 3 must be preliminarily subjected toangular adjustment so that the three beams, specifically the zero-orderbeam, the +first-order beam, and the −first-order beam are alignedstrictly in a straight line in either an X-axis or a Y-axis direction.In the present embodiment, the +first-order beam, and the −first-orderbeam are used for explanation, but higher-order diffracted light beamsmay alternatively be used.

The PD assembly 1 shown in FIG. 3 has eight PD's arranged at its lightreceiving face (encircled by a chain line). The PD assembly 1 is shownin detail in FIG. 4. Referring to FIG. 4, the aforementioned eight PD's(1 a to 1 h) are arranged at the light receiving face of the PD assembly1, and light emitted from the LED 2 falls incident on the lightreceiving face. The PD's 1 a, 1 b, 1 c and 1 d constitute a first lightreceiving element group, and the PD's 1 e, 1 f, 1 g and 1 h constitute asecond light receiving element group consisting of two isolated clusterssandwiching the first light receiving element group. The optical axis ofthe light incident on the light receiving face is oriented perpendicularto the light receiving face, and it is preferred that the center of thezero-order beam be positioned at the center of an area occupied by thePD's 1 a to 1 d (the first light receiving element group), the center ofthe +first-order beam be positioned at the center of an area occupied bythe PD's 1 e and 1 f (one cluster of the second light receiving elementgroup), and that the center of the −first-order beam be positioned atthe center of an area occupied by the PD's 1 g and 1 h (the othercluster of the second light receiving element group). In the opticaldisplacement sensor according to the first embodiment, rotationaladjustment around a Z-axis (oriented perpendicular to the lightreceiving face of the PD assembly 1) is performed based on positionalrelation between the above-described light receiving face of the PDassembly 1 and respective beams (the zero-order, +first-order, and−first-order beams).

A method of rotational adjustment about the Z-axis will be describedwith reference to FIGS. 5A to 5F. Referring first to FIGS. 5A to 5C, thezero-order, −first-order beam, and +first-order beams are denoted by 2a, 2 b and 2 c, respectively. And, symbols A to H in FIGS. 5A to 5Fdenote intensities of lights received at the PD's 1 a to 1 h,respectively. In the first embodiment, the positional relation betweenthe PD assembly 1 and the LED 2 is adjusted with respect to rotationaldirection about the Z-axis based on difference between the total of theintensities F and G and the total of the intensities E and H. Thisadjustment is preferably performed by rotating the PD assembly 1 whichis structured to be rotatable about the center of the first lightreceiving element group, specifically the PD's 1 a to 1 d.

When the zero-order beam 2 a, the −first-order beam 2 b, and the+first-order beam 2 c impinge on the PD assembly 1 as shown by FIG. 5A,the total intensity of F+G minus the total intensity of E+H leaves apositive value as shown by FIG. 5D. In such a case, the PD assembly 1 isrotated in a direction so as to cancel −θ shown in FIG. 5A.

When the zero-order beam 2 a, the −first-order beam 2 b, and the+first-order beam 2 c impinge on the PD assembly 1 as shown by FIG. 5B,the total intensity of F+G minus the total intensity of E+H leaves azero value as shown by FIG. 5E. This indicates that the PD assembly 1and the LED 2 are appropriately positioned to each other with respect tothe rotational direction about the Z-axis, and the PD assembly 1 doesnot have to be rotated in either direction.

When the zero-order beam 2 a, the −first-order beam 2 b, and the+first-order beam 2 c impinge on the PD assembly 1 as shown by FIG. 5C,the total intensity of F+G minus the total intensity of E+H leaves anegative value as shown by FIG. 5F. In such a case, the PD assembly 1 isrotated in a direction so as to cancel +θ shown in FIG. 5C.

FIG. 6 shows another PD assembly 10 for the first embodiment, whichreplaces the PD assembly 1 shown in FIG. 4. The PD assembly 10 has PD's10 a to 10 d, in place of the PD's 1 a to 1 d, which constitute a firstlight receiving element group, PD's 11 a to 11 d, in place of the PD's 1e and 1 f, which constitute one cluster of a second light receivingelement group, and PD's 12 a to 12 d, in place of the PD's 1 g and 1 h,which constitute another cluster of the second light receiving elementgroup. In the embodiment, the second light receiving element group maybe constituted any number of PD's provided that two clusters thereofsandwiching the first light receiving element group respectively have aplurality of PD's. The PD assembly 10 and the LED 2 can be positioned toeach other with respect to rotational direction about the Z-axisfollowing the method explained with reference to FIGS. 5A to 5F.

A second embodiment of the present invention will be described withreference to FIGS. 2, 8, and 9A to 9F. Referring to FIG. 7, an opticaldisplacement sensor according to the second embodiment comprises a PDassembly 15 as a light receiving means, and a laser source 16 as a lightsource. Light emitted from the laser source 16 has its light intensitydistribution shaped oval in cross section with two axes of symmetrycrossing at right angles, and this distribution shape is leveraged intothe optical displacement sensor according to the second embodiment.

Referring to FIG. 8, the PD assembly 15 is of a conventional structure,specifically has four PD's 15 a to 15 d arranged at its light receivingface, and light 16 a emitted from the laser source 16 impinges on thelight receiving face of the PD assembly 15. The optical axis of thelight 16 a is oriented perpendicular to the light receiving face, and itis preferred that the center of the light 16 a be positioned at thecenter of an area occupied by the PD's 15 a to 15 d so that respectivelight intensities at the PD's 15 a to 15 d are equal to one another. Inthe optical displacement sensor according to the second embodiment,rotational adjustment about a Z-axis (oriented perpendicular to thelight receiving face of the PD assembly 15) is performed based onpositional relation between the above-described light receiving face ofthe PD assembly 15 and the light 16 a.

A method of rotational adjustment about the Z-axis will be describedwith reference to FIGS. 9A to 9F, wherein symbols A to D denoteintensities of lights received at the PD's 15 a to 15 d, respectively.In the second embodiment, the positional relation of the PD assembly 15relative to the laser source 16 with respect to rotational directionabout the Z-axis is adjusted based on difference between the total ofthe intensities A and C and the total of the intensities B and D. Thisadjustment is preferably performed by rotating the PD assembly 15 whichis structured to be rotatable about the center of the first lightreceiving element group, specifically the PD's 15 a to 15 d.

When the light 16 a impinges on the PD assembly 15 as shown by FIG. 9A,the total intensity of A+C minus the total intensity of B+D leaves apositive value as shown by FIG. 9D. In such a case, the PD assembly 15is rotated in a direction so as to cancel −θ shown in FIG. 9A.

When the light 16 a impinges on the PD assembly 15 as shown by FIG. 9B,the total intensity of A+C minus the total intensity of B+D leaves azero value as shown by FIG. 9E. This indicates that the PD assembly 15and the laser 16 are appropriately positioned to each other with respectto the rotational direction about the Z-axis, and the PD assembly 15does not have to be rotated in either direction.

When the light 16 a impinges on the PD assembly 15 as shown by FIG. 9C,the total intensity of A+C minus the total intensity of B+D leaves anegative value as shown by FIG. 9F. In such a case, the PD assembly 15is rotated in a direction so as to cancel +θ shown in FIG. 9C.

A third embodiment of the present invention will be described withreference to FIG. 10. An optical displacement sensor according to thethird embodiment comprises a PD assembly 15 (same as employed in thesecond embodiment) as a light receiving means, an LED 2 (same asemployed in the first embodiment) which is a light emitting element as alight source, and a cylindrical lens 17 disposed between the PD assembly15 and the LED 2.

Light emitted from the LED 2, which originally is not shaped oval incross section, has its cross section modified into an oval configurationwith two axes of symmetry when passing through the cylindrical lens 17,and is received at the light receiving face of the PD assembly 15. Sincethe PD assembly 15 is structured in the same way as in the secondembodiment, and since the light received by the PD assembly 15 has anoval cross section like in the second embodiment, rotational adjustmentabout the Z-axis can be performed following the method described in thesecond embodiment, and an explanation thereof is omitted.

In the foregoing embodiments, a light receiving means is mounted at oneof a reference object and a measurement object, and a light source ismounted at the other one thereof, but the present invention is notlimited to this structure but may be applied to a structure which isdisclosed in Japanese Patent Application No. 2003-299827 by the presentinventors, filed claiming priority to Japanese Patent Application No.2003-141421, and in which both a light receiving means and a lightsource are mounted together at one of a reference object and ameasurement object, and a reflector is mounted at the other one thereofat which the light receiving means and the light source are not mounted,wherein light emitted from the light source is reflected backward bymeans of two or three reflection surfaces of the reflector and receivedby the light receiving means, whereby the positional displacement of themeasurement object relative to the reference object with respect totwo-axis directions in a plane perpendicular to the optical axis of thelight emitted from the light source can be measured. Further, thepresent invention can be applied to any optical displacement sensor withwhatever structure disposed between a light receiving means and a lightsource.

In the first embodiment of the aforementioned Japanese PatentApplication No. 2003-299827, as explained with reference to FIG. 7therein, the direction in which the two reflection surfaces of thereflector oppose each other is set to an intermediate direction orientedso as to make a 45 degree angle to both of the two axes (X-axis andY-axis) with respect to which displacement is to be detected by anoptical sensor unit (optical displacement sensor) thereby enabling theoptical sensor unit to detect displacement with respect to the two axes(X- and Y-axes). Accordingly, for example, when the second or thirdembodiment of the present invention, which leverages the oval-shapedintensity distribution of light emitted from the light source, isapplied to the optical displacement sensor employing a reflector withtwo reflection surfaces as described in the first embodiment of theaforementioned Japanese Patent Application No. 2003-299827, it ispreferred that the two symmetry axes of the oval configuration bearranged so as to make a 45 degree angle to the two-axis directions withrespect to which displacement is measured by the optical displacementsensor. In this connection, when the second or third embodiment of thepresent invention is applied to the optical displacement sensoremploying a reflector with three reflection surfaces as described in thesecond embodiment of the aforementioned Japanese Patent Application No.2003-299827, the axis arrangement described above is not required asunderstood from FIG. 11 therein.

The present invention can be applied to measurements of various physicalquantities detectable on the basis of displacement, in addition to theabove-described external force detecting devices such as six-axis forcesensors.

While the present invention has been illustrated and explained withrespect to specific embodiments thereof, it is to be understood that thepresent invention is by no means limited thereto but encompasses allchanges and modifications that will become possible within the scope ofthe appended claims.

1. An optical displacement sensor comprising: a light source disposed atone of a reference object and a measurement object; a light receivingmeans disposed at the other one thereof at which the light source is notdisposed, and functioning to receive light emitted from the light sourcethereby measuring displacement of the measurement object relative to thereference object with respect to two-axis directions in a planeperpendicular to an optical axis of the light emitted from the lightsource, the light receiving means including a first light receivingelement group centrally located, and a second light receiving elementgroup constituted by two separate clusters disposed so as to sandwichthe first light receiving element group; and a light diffracting elementdisposed between the light source and the light receiving means, andfunctioning to diffract the light emitted from the light source into azero-order beam, and higher-order beams along one direction of thetwo-axis directions, such that the zero-order beam is received at thefirst light receiving element group, and the higher-order beams arereceived at the second light receiving element group.
 2. An opticaldisplacement sensor comprising: a light source disposed at one of areference object and a measurement object; and a light receiving meansdisposed at the other one thereof at which the light source is notdisposed, and functioning to receive light emitted from the light sourcethereby measuring displacement of the measurement object relative to thereference object with respect to two-axis directions in a planeperpendicular to an optical axis of the light emitted from the lightsource, wherein the light emitted from the light source, at least whenreceived at the light receiving means, has its intensity distributionshaped in an oval configuration with two symmetry axes oriented so as tomatch the two-axis directions, respectively, with respect to which thedisplacement of the measurement object relative to the reference objectis measured.
 3. An optical displacement sensor comprising: a lightsource disposed at one of a reference object and a measurement object; areflector member disposed at the other one thereof at which the lightsource is not disposed; a light receiving means disposed at the oneobject at which the light source is disposed, and functioning to receivelight which is emitted from the light source and which impinges on thereflector member to be reflected backward, thereby measuringdisplacement of the measurement object relative to the reference objectwith respect to two-axis directions in a plane perpendicular to anoptical axis of the light emitted from the light source, the lightreceiving means including a first light receiving element groupcentrally located, and a second light receiving element groupconstituted by two separate clusters disposed so as to sandwich thefirst light receiving element group; and a light diffracting elementdisposed at an optical path from the light source to the light receivingmeans via the reflector member, and functioning to diffract the lightemitted from the light source into a zero-order beam, and higher-orderbeams along one direction of the two-axis directions, such that thezero-order beam is received at the first light receiving element group,and the higher-order beams are received at the second light receivingelement group.
 4. An optical displacement sensor comprising: a lightsource disposed at one of a reference object and a measurement object; areflector member disposed at the other one thereof at which the lightsource is not disposed; and a light receiving means disposed at the oneobject at which the light source is disposed, and functioning to receivelight which is emitted from the light source and which impinges on thereflector member to be reflected backward, thereby measuringdisplacement of the measurement object relative to the reference objectwith respect to two-axis directions in a plane perpendicular to anoptical axis of the light emitted from the light source, wherein thelight emitted from the light source, at least when received at the lightreceiving means, has its intensity distribution shaped in an ovalconfiguration with two symmetry axes oriented so as to match thetwo-axis directions, respectively, with respect to which thedisplacement of the measurement object relative to the reference objectis measured.
 5. An optical displacement sensor according to claim 2,wherein the light source is constituted by a light emitting diode (LED),and a cylindrical lens is disposed between the LED and the lightreceiving means whereby the light emitted from the LED has its intensitydistribution turned into the oval configuration with two symmetry axes.6. An optical displacement sensor according to claim 1, wherein thelight receiving means is structured to be rotatable about the firstlight receiving element group.
 7. A method of adjusting an opticaldisplacement sensor which comprises: a light source disposed at one of areference object and a measurement object; a light receiving meansdisposed at the other one thereof at which the light source is notdisposed, and functioning to receive light emitted from the light sourcethereby measuring displacement of the measurement object relative to thereference object with respect to two-axis directions in a planeperpendicular to an optical axis of the light emitted from the lightsource, the light receiving means including a first light receivingelement group centrally located, and a second light receiving elementgroup with two separate clusters disposed so as to sandwich the firstlight receiving element group; and a light diffracting element disposedbetween the light source and the light receiving means, and functioningto diffract the light emitted from the light source into a zero-orderbeam, and higher-order beams along one direction of the two-axisdirections, such that the zero-order beam is received at the first lightreceiving element group, and the higher-order beams are received at thesecond light receiving element group, the method comprising a step ofadjusting a position of the light receiving means relative to the lightsource with respect to a rotational direction about the optical axis ofthe light emitted from the light source based on a reception state ofthe higher-order beams at the second light receiving element group.
 8. Amethod of adjusting an optical displacement sensor which comprises: alight source disposed at one of a reference object and a measurementobject; and a light receiving means disposed at the other one thereof atwhich the light source is not disposed, and functioning to receive lightemitted from the light source thereby measuring displacement of themeasurement object relative to the reference object with respect totwo-axis directions in a plane perpendicular to an optical axis of thelight emitted from the light source, wherein the light emitted from thelight source, at least when received at the light receiving means, hasits intensity distribution shaped in an oval configuration with twosymmetry axes, the method comprising a step of adjusting a position ofthe light receiving means relative to the light source with respect to arotational direction about the optical axis of the light emitted fromthe light source based on a reception state of the light at the lightreceiving means.
 9. A method of adjusting an optical displacement sensorwhich comprises: a light source disposed at one of a reference objectand a measurement object; a reflector member disposed at the other onethereof at which the light source is not disposed; a light receivingmeans disposed at the one object at which the light source is disposed,and functioning to receive light which is emitted from the light sourceand which impinges on the reflector member to be reflected backward,thereby measuring displacement of the measurement object relative to thereference object with respect to two-axis directions in a planeperpendicular to an optical axis of the light emitted from the lightsource, the light receiving means including a first light receivingelement group centrally located, and a second light receiving elementgroup with two separate clusters disposed to as to sandwich the firstlight receiving element group; and a light diffracting element disposedat an optical path from the light source to the light receiving meansvia the reflector member, and functioning to diffract the light emittedfrom the light source into a zero-order beam, and higher-order beamsalong one direction of the two-axis directions, such that the zero-orderbeam is received at the first light receiving element group, and thehigher-order beams are received at the second light receiving elementgroup, the method comprising a step of adjusting a position of the lightreceiving means relative to the light source with respect to arotational direction about the optical axis of the light emitted fromthe light source based on a reception state of the higher-order beams atthe second light receiving element group.
 10. A method of adjusting anoptical displacement sensor which comprises: a light source disposed atone of a reference object and a measurement object; a reflector memberdisposed at the other one thereof at which the light source is notdisposed; and a light receiving means disposed at the one object atwhich the light source is disposed, and functioning to receive lightwhich is emitted from the light source and which impinges on thereflector member to be reflected backward, thereby measuringdisplacement of the measurement object relative to the reference objectwith respect to two-axis directions in a plane perpendicular to anoptical axis of the light emitted from the light source, wherein thelight emitted from the light source, at least when received at the lightreceiving means, has its intensity distribution shaped in an ovalconfiguration with two symmetry axes, the method comprising a step ofadjusting a position of the light receiving means relative to the lightsource with respect to a rotational direction about the optical axis ofthe light emitted from the light source based on a reception state ofthe light at the light receiving means.
 11. An external force detectingdevice comprising at least one optical displacement sensor structured asdescribed in claim 1, wherein an external force applied to a measurementobject is detected based on a signal containing a measurement result bythe at least one optical displacement sensor.
 12. An external forcedetecting device according to claim 11, comprising two or more of theoptical displacement sensors, wherein the two or more opticaldisplacement sensors detect respective displacements with respect totwo-axis directions different from one another.